A problem that exists in the art is to provide optical couplers that efficiently communicate light to or from an optical fiber bus. Many factors effect this efficiency, but the most important factor is the need to match the size and shape of the exit pupil of light emerging from the optical fiber bus to the acceptance shape of the optical coupler fiber in the optical coupler. For a circular optical coupler fiber, the acceptance shape is a cone resulting in the exit pupil also being a cone. The optical coupler fiber is also referred to as a launch tap, drop tap, or collection fiber.
Mechanical stripping methods are known for fabricating the coupler openings in the cladding. These methods remove the cladding by physically scraping the cladding from the core. In addition, chemical etching methods have been utilized to remove the cladding from the optical core. Both mechanical stripping and chemical etching methods are limited because of their inability to fabricate the correct coupling opening size and shape. In fact, no attempt has been made with these methods to match the exit pupil of the emerging light with the acceptance shape of the coupler fiber.
U.S. PAT. NO. 4,626,652 discloses a method for fabricating optical couplers that utilizes a laser to remove nearly all of the cladding from a fiber. The laser beam scans back and forth across the region resulting in the removal of a linear portion of the cladding. Using this method, two optical fibers are prepared and are fused together by applying heat, forming an optical coupler. Again, no attempt is made to match the exit pupil of emerging light with the acceptance shape of the coupler fiber.